What is the use of Position Column Name in USER_CONS_COLUMNS Table

Question

Please let me know the purpose of POSITION Column Name in USER_CONS_COLUMNS Table.
Example :
Created this below Table having two constraints 1.Primary Key 2.Check Constraint
CREATE TABLE A(ID NUMBER PRIMARY KEY,NAME VARCHAR2(30),SAL NUMBER CHECK (SAL > 0))
When i execute the below query
SELECT POSITION,CONSTRAINT_NAME FROM USER_CONS_COLUMNS WHERE TABLE_NAME = 'A'
it displays the data :
POSITION CONSTRAINT_NAME
1 SYS_C005488
SYS_C005487
Only for the first record it displays the POSITION but not for the second row.
Kindly help me on this.

Answer 1

SQL> CREATE TABLE A(
  2     ID1 NUMBER
  3   , ID2 NUMBER
  4   , NAME VARCHAR2(30)
  5   , SAL NUMBER CONSTRAINT A_SAL_POSITIVE CHECK (SAL > 0)
  6   , CONSTRAINT A_PRIMARY_KEY PRIMARY KEY (ID1, ID2)
  7  )
  8  /
Table created.
SQL> SELECT CONSTRAINT_NAME, POSITION, COLUMN_NAME
  2    FROM USER_CONS_COLUMNS
  3   WHERE TABLE_NAME = 'A'
  4   ORDER BY CONSTRAINT_NAME, POSITION
  5  /
CONSTRAINT_NAME                  POSITION COLUMN_NAME
A_PRIMARY_KEY                           1 ID1
A_PRIMARY_KEY                           2 ID2
A_SAL_POSITIVE                            SALA primary key constraint can have multiple columns - the position shows the order the columns are in the primary key definition (and thus also in the pk supporting index.)
A check constraint does not have any such ordering of the columns involved, so therefore position is null.